The invention disclosed herein pertains to a die for crimping bullets in ammunition cases in connection with reloading spent cases.
Reloading spent ammunition cases typically involves removing and replacing the spent primer cap in the head of the case. After that step there is usually a shaping of the mouth end and possibly the body portion of the case. The case is then filled with a predetermined quantity of powder and a bullet is inserted in the open end or mouth. The neck is then crimped to secure the bullet. A roll crimp is used on most hand loaded ammunition. The mouth of the case is rolled into the bullet crimping groove by pushing the case against an angled shoulder within a bullet seating die. This is exemplified in U.S. Pat. No. 4,385,546 which shows a die used for forcing the bullet into the mouth of the case. As the ammunition case with a bullet set in it is forced into the die, the bullet strikes a stop which pushes the bullet into the case to the proper depth and, when it reaches the proper depth, the very edge of the mouth of the case encounters an annular tapered shoulder which rolls the edge of the mouth into the bullet.
When the hand loader crimps in this manner, tightness of the bullets is usually far from being as uniform as is obtained by the original manufacturer. A uniform and firm crimp is desirable for ammunition that is subject to rough handling such as when it is handled by hunters or carried in their pockets. If the crimp is not firm the bullet may become misaligned or loosened. The result is that the start or initial pressure generated by ignition of the powder in the case will not be uniform in which case accuracy of the bullet is decreased. Those who reload their own ammunition know that the most important factor for accuracy is a uniform start pressure. Until the present invention was made, hand loaders had to obtain a uniform start pressure by seating the bullet so that it would just touch or nearly touch the rifling in the breech of the gun. Manufacturers supply ammunition originally which has a uniform start pressure because the crimp on the bullet is uniform. Tests have demonstrated that bullets crimped properly, that is, uniformly and with sufficient gripping force, have less velocity variation.
The conventional roll crimp leaves much to be desired in that case length must be very uniform to secure a uniform sound crimp. If the crimp die is incorrectly adjusted, excessive axial force on the case mouth can bulge the case just behind the crimp or push out the shoulder of the case. It is because there is relative motion between the mouth of the case and the die in conventional crimping dies that this accidental overcrimping and bulging of the case body and the neck of the case occurs.